We first encountered this last back end.
My son shot a nice 6 point Sika and I shot a Red spiker. We were on forestry blocks a couple of miles apart.
Neither animal showed any lameness or obvious poor health. The grallochs looked totally normal and healthy too. Both beasts were well fleshed and apart from tick infestation they seemed just normal. Where we shoot heavy tick infestation is pretty normal.
Only when butchering did we find puss filled little lesions (raisin to grape sized) distributed through out their muscles. I showed this to my local vet. He wasn't certain but said it looked to him like Tick Pyaemia and from my description of the beasts pre-mortem he reckoned they'd probably had it for a while without joint problems and were well on course to recover naturally.
We disposed of the carcasses and they did not go into the food chain.
Anyone else know more about this disease? I have googled it but we're more interested in first hand experience.